Milling machine transmission and control mechanism



March 2 1937. w. WRIGI-IT MILLING MACHINE TRANSMISSION AND CONTROLMECHANISM 5 Sheets-Sheet 1 Filed Jan. 2, 1935 w w 1.99M W w 2% 4/ W M g720/ o v w /9a Null 1" V 7.; y 25: aw /9 ujq 4 .lvw W6 I V I I V 0' VLE/qH w. WRIGHT March 2, 1937. L. w. WRIGHT 2,072,540

MILLING momma TRANSMISSION AND CONTROL MECHANISM Filed J an. 2,1955 '5Sheets-Sheet 2.

QW LE/qu MWRIGHT L. W. WRIGHT March 2, 1937.

MILLING MACHINETRANSMISSION AND CONTROL MECHANISM Filed Jan. 2, 1935 5Sheets-Sheet 3 M s I z z 7. a Z/MZ 6 a it I 0 m m s a m I w 5 z we 9 0 99 a N. M m 3 I m March 2, 1937. 1.. w. WRIGHT MILLING MACHINETRANSMISSION AND CONTROL MECHANISM Filed Jan. 2, 1935 5 Sheets-Sheet 4Lf/6H N. WEIGHT March .2, 1937... 1, w. WRIGHT MILLING MACHINETRANSMISSION AND CONTROL MECHANISM I Filed Jim. 2, 1935 5 Sheets-Sheet 5W H m W MW 5 L Patented- Man 2, 1937 I UNITED STATES MILLING MACHINETRANSMISSION AND CONTROL MECHANISM Leigh W. Wright, Norwood, Ohio,assignor to The Cincinnati Milling Machine 00., Cincinnati,

Ohio, a corporation of Ohio Application 1m 2', 1935, Serial No. 111

33 Claims.

This invention relates to machine tools and more particularly toimproved transmission and control mechanism therefor.

One ofthe objects of this invention is to im- 5 prove, the operation andcontrol of machine tools in such a manner that the feed rate of a movingpart may be automatically varied by trip dogs as often as desired, andto any'desired value within the range of the feed transmission during itcontinuous movement of the part.

Another object of this invention is to place the feed rate determinationof a 'machine tool under control of trip dogs whereby any given cycle ofvariable feed rates may be predetermined at the 15 time the machine isset up for its cycle of operation.

A further object of this invention is to eliminate the necessity andcost of providing feed rate control cams for variable feed cycles and toproduce a .control mechanism having a given set of parts which may besuitably prepositioned to yield any variable feed rate cycle of whichthe transmission is capable.

An additional object of this invention is to pro- 25 vide anelectrically driven milling machine in which direct current motors maybe utilized with an alternating'current source so that variable ratesmay be obtained directly by varying the speed of the motor, thuseliminating the neces- 30 sity of cumbersome and expensive variablespeed gear boxes.

' A still further object of this invention is to produce a simplifiedcontrol for milling machines having a limited number of parts, butcapable 35 of yielding new and improved results.

Other objects and advantages of the present invention should be readilyapparent by reference to the following specification, considered inconjunction with the accompanying drawings form- 40 ing a part thereofand it is to be understood that any modifications may be made in theexact structural details. there shown and described, within the scope ofthe appended claims, without departing from or exceeding the spirit ofthe 45 invention. 7

By referringto the drawings in which like or similar reference numeralsindicate like or similar parts: j

Figure l is an elevation'of a machine tool embodying the principles ofthis invention. Figure 2 is a sid'erelevatiomof the machine shown inFigure 1 as viewed from. the left hand side of that figure and withparts broken away to show the spindle transmission.

selector mechanism and the driving connections.

Figure 4 is a section on the line 4--4 of Figure 1 showing thearrangement of the trip control mechanism.

Figure5 is a detail section on the line 5--5 of 5 Figure 45.

Figure 6 is a section on the line B6 of Figure 1.

- Figure 7 is a detailed section-on the line ll-l of Figure 1.

Figure 8 is a detailed section on the line t-- of Figure 6.

Figure 9 is an enlarged view showing the constructional details of theratchet clutch mechanism associated with one of the trip plungers.

Figure 10 isa detailed View of one of the control dogs as viewed on theline [It-Ml of Figure 4.

Figure 11 is a rear view of the machine shown in Figure 1 with partsbroken away to show the arrangement of the various prime movers. 0

- Figure 12 is an expanded view showing the 2 transmission train forconnecting the feed-rapid traverse selector to the movable elements ofthe machine.

Figures 13 and I l are views showing difierent dog set-ups for yieldingdifferent feed cycles. 7 Figure 15 is an electrical diagram of thecircuit by which a direct current driving motor may be connected toan-A. C. source.

Figure 16 is a diagram of a control circuit.

Figures 17 and 18 are detail views showing the supplementary manner-ofrate graduating the control dogs.

It is conventional practice in machine tools to provide power operablemeans for effecting what is termed a relative feeding movement betweenthe tool and work piece, which movement is utilized fordoing the actualwork oi removing material and control means for varying this rate ofmovement in accordance with the character and 4:0 amount of material tobe removed during a given stroke between the work and tool.

This is true whether the cutter utilized is of the stationary type, suchas a planing tool, or whether it is of the rotary type, such as amilling cutter. For the purpose of saving time during non-cuttingmovements, which have been termed positioning movements, a high speeddrive is utilized, and trip control means provided whereby themovingpart may be selectively connected thereto for movement at arelatively fast or quick traverse rate; Beyond this automatic selectionbetween two rates, which may be termed feed rate and rapid traverserate, no means has yet been.

V provided in connection with machine tools whereby any one of aplurality of feed rates may be automatically utilized for varying therate of table movement with the exception of the case where control camsare utilized. Control cams, however, are costly and are limited to onecycle, which means different cams must be laid out and produced for eachdiiferent cycle desired. In the present invention a plurality ofsimilar'control dogs are provided for selective positioning at thepoints where changes in feed rate are desired, including an easilyadjustable part prepositioned to yield any feed rate within the range ofthe feeding transmission.

A machine embodying the principles of this invention is shown in Figures1, 2 and 11 and is structurally composed of a column l5 having ver--tical guideways l5 upon one face thereof for receiving and guiding aknee H. The knee is provided with horizontal guideways |3 upon which ismounted a saddle l9 having guideways 20 ex tending transversely to thedirection of guideways l8 for receiving and supporting a work table 2|.A cutter spindle 22 is journaled in the upper part of the column forpower rotating a cutter arbor 23 to which may be keyed a metal removingtool 24. The outboard end of the arbor may be supported by an arborsupport 25 depending from the under side of an overarm 25, which overarmis longitudinally adjusted and supported in suitably formed guideways 21formed on the top of the column.

Power means has been provided for translating the knee, saddle and tablealong their respective paths of movement and comprises two independenttransmissions each actuable by its own prime mover, one of which may betermed the variable feed transmission and the other the rapid traversetransmission. Means are provided for selectively connecting thesetransmissions to a common intermediate power train and selector clutchesindividual to the respective supports for I coupling the same to saidcommon driving means.

The feed transmission comprises a direct current motor 28 mounted in aseparate chamber. 29 formed in the column, Figure 11, which chamber isopen at the rear end of the machine so that the driving pulley 38projects beyond the back face 3| of the column. This pulley is connectedby suitable motion transmitting means, such as the belt 32, to a drivenpulley 33 secured to the end of shaft 34, as more particularly shown inFigure 3. The shaft 34 has a gear couplet 35 secured thereto comprisinga large gear 33 and a pinion 31.

A parallel shaft 38 is journaled in the column and has a gear couplet 39splined thereon and movable by manually operable means, including thehandle 43 and shifter fork 4|, to selectively intermesh the gears 42 and43 of the couplet with gears 35 and 31 respectively. The couplet 39 is aform of back gear for producing a high series or a low series of feedrates.

The shaft 38 has another gear 44 which is fixed- Fixed with the innermember 41 is a clutch member 49 which has clutch teeth 59 formed on oneface thereof for interengagement with simi-' larly formed clutch teeth5| on the slideable clutch member 52 which is splined on the outputshaft 53. The gear 45 and associated parts, including the member 49, aremounted for free rotation on a fixed sleeve 54 in which the shaft 53 isjournaled. The clutch 52 is shifted by a shifter fork 55 secured to theshaft 55, which has an operating handle 51 on the exterior of themachine. The member 49 is really an overrunning clutch member and theclutch 52 is therefore normally in engagement therewith at all times sothat when the shaft 53 is driven at a faster rate by the rapid traversetransmission, to be explained hereafter, a member 49 will overrun withrespect to the member 41.

The rapid traverse transmission consists of a prime 'mover 58 mounted ina chamber 59 formed in the column, which has a bevel gear 59 secured tothe end of the armature shaft 5| thereof which gear intermeshes with abevel gear 52 keyed to the end of the upwardly extending shaft 53.

The shaft 53, as shown in Figure 3, is connected by a pair of bevelgears 54 to shaft 55, which is journaled in the column parallel to shaft34. A spur gear 55 is fixed to the end of shaft 55 and drives the finalgear 51 of the rapid traverse transmission. This gear is journaled inanti-friction bearings 58 and is connectable to shaft 53 by a multipledisc friction clutch indicated generally by the reference numeral 59.This clutch is operated by a shifter 10 having a shifter fork 1| pinnedor otherwise securely fastened to shifter rod 12.

The shifter rod is slideably mounted in a solenoid 13 wherebyenergization of the solenoid will cause engagement of the rapid traverseclutch. A spring 14 is interposed between the end of the solenoid andthe shifter fork 1| for normally maintaining the rapid traverse clutchdisengaged. Energization of the solenoid may be controlled by themanually operable switch 15 or the automatically controlled switch 18.These switches are in parallel so that closing of either one will effectengagement of the rapid traverse clutch.

It will now be obvious that the shifter 1| constitutes a feed rapidtraverse selector because upon movement in one direction the rapidtraverse transmission is connected to shaft 53, and

upon movement in the other direction it permits the feed clutch tobecome effective to rotate shaft 53 at a feed rate.

The shaft 53 is operati ely connected by a pair of bevel: gearsindicated generally by the reference numeral 11 to a vertical shaft 18,which, as shown in Figure 12, has ,a spline connection with a spur gear19 journaled in a bracket carried by the knee H. The spline connectionthus maintains an operative connection between the shaft and gear forall vertical movements of the knee. The gear 19 interengages with a spurgear which drives a pair of bevel gears indicated by the referencenumeral 32, which, in turn, rotate tln ough the shaft 33, the gear 34. Aspline shaft is journaled in the knee parallel to shaft 83 and has agear 85 on one end meshing with gear 34 and a bevel gear 31 splinedthereon for actuating the table. The gear 31 is journaled in the saddleand therefore is movable longitudinally of shaft 85 in accordance as thesaddle is moved. The gear 81 drives through the bevel gear 33, shaft 39and bevel gear 33, a pair of bevel gears 9| and 92 in oppositedirections. The gears 9| and 92 are mounted for free rotation withrespect to the table lead screw 93 and are alternately connectablethereto by intermediate clutch member 94 which has a splined connectionwith the lead screw and clutch teeth on opposite ends forinterengagement with clutch teeth on the opposing faces of the gears.This constitutes a reversing mechanism for the table.

As shown in Figure 5, the clutch 94 has a. shifter arm 95 which is'flxedto the shifter rod 96, which in turn is slideably supported at oppositeends in a pair of solenoids 91 and 9t respectively. Springs 99 areinterposed between the ends of respective solenoids and the shifter arm95 for normally maintaining the clutch in a central position and aspring pressed detent I serves to aid in this connection. It will beobvious that upon energization of either solenoid 91 or 98 that theclutch will be shifted in opposite directions, and upon de-energizationof both solenoids, that the springs 99 and the detent member will serveto position the clutch in a central or neutral position.

The gear 86 in Figure 12 drives gear llll, which is directly intermeshedwith spur gear I02 and indirectly connected through idler lllt to gear lM whereby the gears I02 and lll l will be rotated in oppositedirections. These gears have clutch teeth formed on opposing facesthereof which are selectively engageable by the shifter clutch memberI05 which constitutes the reversing clutch for the saddle drive shaftltd to which the saddle member M5 is splined.

The gears i114 and I02 rotate respectively a pair of gears llll and m8journaled for free rotation on the knee elevating screw drive shaft I09and have clutch teeth formed on opposing faces for interengagement withsimilarly formed clutch teeth of the shiftable clutch member llt splinedon shaft Hill. The clutch llll constitutes a reverser for determiningthe direction of movement of the knee, the shaft ltd being connectedwith the knee elevating screw ill by a pair of bevel gears indicatedgenerally by the reference numeral ill.

The electrical circuit by which the direct current motor 2% is connectedto an alternating current source is shown in Figure and the particularform of this circuit does not constitute a part of the presentinvention, it being understood that any suitable form of circuit may besubstituted therefor. Since the details of the circuit and its manner ofoperation are more fully described and explained in a co-pendingapplication of W. H. Howe for Voltage regulation and circuits therefor,Serial No. 668,582, filed in the United States Patent Qflice on April29, 1933, it will be only briefly described herein.

The input power is supplied at 220 volts, 60 cycles, 3 phase,represented by the leads ll t, lid and llb. These leads are Y-connectedrespectively to auto transformers lit, ill and lid.

More particularly, they are connected to the low" potential taps lit,ltll and iii of these-transformers whereby the output voltage isincreased over the input voltage. The output of one leg of each of thetransformers is connected to a common line ltt which leads to thenegative terminal lid of the motor armature lit. The high voltage from.the other leg of these transformers goes through lines lit, lit and mlto plates lit, lit and l 30 respectively of power rectifier tubes lltl,lit and lit. The line lf'l has a series transformer lllfl therein whichoperates the compounding circuit connected thereto.

transformer I39. 'I'he cathodes I40, Ill and I42 of the respective tubesare connected as by a common lead 3 to the positive terminal I of themotor armature I24. Thus the main power circuit is from the commoncathode connections of the tubes l3l, H2 and l33 through the motorarmature back to the common point of the Y- connected transformers IIB,ill and lit, through these transformers to the respective plates of therectifier tubes and back to the common cathode connection. This providesa source of rectifled current for the armature of motor 2t.

Another circuit provides rectified current for the motor field circuitand control system therefor and comprisesanother secondary N5 ofauxiliary transformer l39 having two terminals M6 and ill. The terminalM6 is connected by a line through a filter choke coil lit to thepositive side of the motor field l54. The negative side of the fieldcoil is connected by line l55 and current limiting resistor l56 toterminal l4?! of the secondary M5. A condenser llil is connected acrossthe leads Hi5 and lab. The supply for the motor field thus consists ofthe transformer secondary t lt, the tube -l lll,.the cholre coil ltd,the condenser l all which, in turn, is connected to the terminal llll ofthe coil M5. Across this circuit is connected the output circuit for themotor held, one end of the held being connected to one side of thecondenser lull and the other end of the field being connected throughthe resistor ltt to the other, side of the condenser lt'l.

Across this output circuit is connected the direct current controlcircuit which includes a choke coil llit connected to line ltd andthereby to the positive side of the motor field coil and a condenserlllt, which in turn is connected to line field coil. There is alsoconnected to the choke coil the positive .end of the main speed controlpotentiometer or rheostat l tl. The negative end of this potentiometeris connected part-way of the resistor ltt which limits the field currentof the motor. The adjustable slider lllt of the potentiometer, which maycorrespond to the rotating arm of a rheostat, connects the potentiometerto the armature filter comprising an iron core inductance llit and theresistance ltd which are arranged in' series, the lead l lit from theslider ltd being connected to their common point ltd. The other end ofthe inductance is connected to the negative terminal of the motorarmature and the other end of the resistance ltd is connected to thepositive terminal of the motor armature ltd. This system thus transmitsthe direct current potential of the armature but blocks the alternatingcurrent potential.

0 In addition to the above circuits there is a compounding circuit whichderives its input from the series transformer lt l, previously referredto, and the output from this transformer through the secondary llll'l isproportional to the alternating component, and hence the direct currentoutput of the rectifier tube ll t, and since the rectifier tubes ltl,l3? and l3t share the load equally it is proportional to the totaloutput current. The outer ends of the winding I61 are connected to thetwo plates "38 and I 69 of the fullrwave rectifying output lid. Thefilament ill of this tube connects more positive side of a filtercircuit comprising two condensers Ill and I13 and the inductance I'I4.Across the condenser I13 is connected the auxiliary or-compoundingpotentiometer which comprises the two resistors I15 and I18. Theresistance I15 is fixed and the resistance I13 is provided with a sliderIll. The negative end of this potentiometer connects through the leadI13 with the point I19 of the fixed divider resistances I80 and IBI andthe slider E connects through the lead I82 with the phasing transformersecondaries I33, I34 and I85.

The potential of point I66 is negative with respect to the potential ofthe line I43 by an amount equal to the direct current potential acrossthe armature of the motor. The potential of the point I86 is positivewith respect to the potential of the point I66 by an amount proportionalto the setting of the slider I62 of the main speed control potentiometerI". When the slider is at the positive end this voltage is zero; whenthe slider is at the negative end this voltage is at its maximum. Thepotential at the point I19 is negative with respect to the potential ofthe point I86 by a fixed amount, in the present instance about 20 voltsdetermined by the ratio of resistances I30 and I8I and the directcurrent potential of the control circuit. The potential of the point ofthe slider I" is positive with respect to the potential of the point I19by an amount proportional to the current flow in the armature of themotor. Thus, the direct current potential applied to the grids of thetubes I3I, I32 and I33, which is substantially the same as the potentialof the point of the slider II'I'as compared with the potential of thecathodes of these tubes, which is the potential of the line I43, isequal tothe sum of the potential of the main speed control potentiometerplus the potential of the compounding circuit minus the sum of the fixedvoltage divider potential plus the voltage on the armature of the motor.Thus the main control is effected by the difference of the motor voltageand the control direct current voltage, any variation in certainconditions being accompanied by a shift of the direct current po'tentialon the grids in such a manner that the plate current flow as controlledby the grids so result in a load voltage having a fixed relation to thecontrolling direct current voltage. To this is added the voltage fromthe compounding circuit so that the difierence between the load voltageand the direct current voltage can be made to vary the load in anydesired fashion, resulting in a load voltage which may be constantregardless of load or which may either increase or decrease as the loadincreases.

The compounding system is a means for' offsetting the effects tending toreduce or increase motor speed. Since the compounding component dependsalmost entirely on current fiow it is equally effective for maintainingconstant motor speed throughout a 20-1 range of motor speed withoutadjusting the system. A control switch I81 completes the circuit betweenthe positive side of the main speed control potentiometer IIiI and thefixed voltage divider and provides for normal operation. When the switchis open this connection is opened, which leaves the voltage divider I80connected to the circuit only at its negative end, which thereby changesthe potential at point I19. This change in potential reacts in such amanner on the rectifying tubes I3I, I32 and I33 that they are preventedfrom passing any current and the armature power is thus cut off from themotor. The electhat it may vary the speed of the motor.

The potentiometer coil may assume arcuate form so that the slider I62may be in the form of a pivoted arm rotatable about a fixed center formovement over the coil. Such a form of potentiometer is enclosed in thecasing I88 shown in Figure 6 of the drawings, and the arm which is notshown is secured to the shaft I89 which passes through the casing I88.The shaft I89- is rotatable through an angle of substantially 270 butthe angle of arcuate movement of the potentiometer slider is a littleless than this.

The reason for this is that the shaft is rotatable through an angle lessthan 270 to effect the full range of feed motor speeds so that uponfinal movement through the last few degrees a circuit may be closed toeffect 'a rapid traverse connection, while the feed motor is stillrunning at its highest rate.

The means for controlling the rotation of shaft I89 and thereby thesetting of the potentiometer will now be explained. A control dog I90,Figure 10, is secured to the front face of the table by means of theusual T-headed bolts I9I and the dogs utilized for controlling the feedrate when the table is moving toward the right have a pivoted latchlever I92 which is beveled on the lower right hand corner as at I93 fordepressing trip plunger I84. Clockwise rotation of the latch member isprevented by a shoulder I95 formed on the upper left hand corner thereofbut the upper right hand corner is rounded as at I96 to permit the latchmember to pass over the plunger I94 when the table is moving toward theleft without depressing the plunger.

Dogs which control the feed rate during movement of the table to theleft are similarly formed with the exception that the member I92 is madeto the opposite hand for operating trip plunger I94 during movement ofthe table to the left, but capable of passing over the trip plungerwithout effecting movement thereof during movement of the table towardthe right. This constitutes two forms of trip dogs which are bothutilized. regardless of the direction of table movement for increasingthe feed rate of the table. In other words, depression of theplunger I94will cause, through mechanism to be explained, upward movement of themain control plunger I91. The amount of this upward movement will dependupon a prepositionable feed rate determinator I98 which is secured tothe front face I99 of the control dog by a T bolt 200 verticallyadjustable in a T slot 2III formed centrally of the face I99.

A second plunger 202 is mounted in front of v the plunger I94 forcooperation with a second pair of latch members similar to the firstpair except that they depend in the plane of the plunger 202 forcooperation therewith and willnot in any way interfere with plunger I94.This last pair of latch members will be carried by separate dogs withthe result that the machine is provided with four different types ofdogs.

to the position shown in Figure 1.

for anygiven position.

Each'dog' will have a diflerent type of latch member with the resultthat there will be one dog for increasing the feed rate 'during move-'ing the-rate ofmovement of the table toward the right, and a fourth dogfor decreasing the rate of table movement toward the left.

The trip plunger I91 has a first lug 203 which projects into the path ofmember I98 when the plunger I91 is rotated clockwise as viewed in planThis rotation is effected by a wing 204 projecting from the side of theplunger in a direction away from the table for cooperation with theencircling fln-' gers 205 of reversing dogs 206. When the plung er I91is rotated clockwise the lug203fiis withdrawn and a second lug-205 movedinto the path of stop I98. The manner of controlling the plunger I91 inorder to determine the feed rate will be more fully understood byreference to Figure 17. In that figure the stop I98 is midway verticallyof the front face of the control dog. When in this position the feedrate is zero.

The dogs which control the feed rate during movement of the table towardthe right have graduations only; on the upper half thereof, as

shown in Figure 17, while the dogs that control' movement of the tableto the left have graduations on the lower half thereof. The reason forthis is that in spite of the fact that the vertical position of theplunger is the same for each of the .given feed rates, yet the upwardand downward movement of the plunger is controlled in one case by theupper lug 203 and in the other case by the lower lug 205. Incidentally,the fact that both of the control dogs which control movement of thetable in one direction have their graduations on the upper half thereofand the control dogs that control the other direction of movement havethe graduations on the lower half thereof, aid in distinguishing thedogs when selecting them during. the set-up of the machine.

Referring to Figure 17 it will be apparent that in order to limit upwardmovement of lug 203 that the member I98 must be placed above the lug andtherefore the position of the lower surface 205 of member I98 is thecontrolling surface and the graduations 206'on the left side of the dogare provided with this idea in mind so that the surface 205 can beplaced in alignment with any -of. the graduations to determine theamount of upward movement and thereby the feed rate effected It willalso be obvious this case the upper surface 20I'of member I90 is now thedetermining surface and therefore the graduations on the right hand sideof the dog are provided so that this surface may be spaced in alignmentwith the graduations. This eliminates the necessity for taking intoconsideration the thickness of lug 203 and making correctionsthererate'the lefthand stal a d t b t o u face that in order to limitdownward movement of the lug 203 that the 'member I98 must be placedbeneath the lug. In

of member I98 must be utilized in setting the member, whereas if the newrate is lower, then the graduations on the right hand side and the uppersurface of member I98 must be utilized in setting the member.

The same thing is true with respect to determining feed rate in theopposite direction except that the control dog has graduations on thelower half thereof as shown in Figure 18 and the member I98 is set aboveor below the lug 205 for limiting the movement thereof. It will be notedthat.

the plunger will have the same vertical position for allrates becausewhether the lug 205 is cooperating with the under side of member I98 asshown in Figure 18, or the lug 203 cooperating with the under side ofmember I98 as shown in Figure 17, the highest feed rate will be obtainedand the plunger will be in the same position vertically.

The particular mechanism for moving plunger I91 will now be explained.The plunger I94 in Figure 9 is reciprocably mounted in a bore 209 andhas a spring 2I0 surrounding a reduced portion 2 I I'thereof forexerting a continuous upward movement of the plunger. The reducedportion 2 projects through a threaded plug 2I2 which closes the. lowerend of the bore 209, forms a shoulder for the lower end of the spring,and acts as an abutment by engagement with lock nuts 2I3 threaded on theend of the reduced portion 2I I. The plunger I94, therefore, alwaysreturns to the same vertical position and automatically after the latchmember has passed over. it.

The member I94 has rack teeth 2I4 formed on one side thereof whichinterengage with the annular gear 2 I5. This gear surrounds a rollerclutch member 2I6 for actuation of shaft 2" in one direction only. Inother words, the balls 2I8 which are equally spaced about the peripheryof member 2I6 are wedged in one direction upon counterclockwise rotationof gear 2I5 to effect rotation of member 2 I6 and thereby of the shaft2". Upon upward movement of plunger I94 by the spring 2I4 the balls aremoved in the opposite direction, thereby freeing the member 2I8 from thegear, and the gear returns without causing rotation of shaft 2I'I. Theplunger 202 is connected by the same form of mechanism for effectingrotation of shaft 2II in a clockwise direction.

The member 2I6 is connected by a friction clutch member 2I9 to a beveledgear 220, the amount of the friction depending upon strength of spring22I. This friction should be great enough to cause movement of theparts, but still weak enough to permit slippage because the downwardstroke of plunger I 94 is always the same, but the amount-of upward ordownward movement of plunger I9! is determined by the position of memberI98. Therefore, the theory -of operation is that the plunger I94 willalways be given the same length of stroke by the latch pawl but theamount of movement that will be imparted to the plunger will be limitedby member I98 and during the remainder of the movement slippage willtake place at the friction clutch. In other words, the downpinion 225.This pinion is integral with shaft 228 which has keyed thereto a spurgear 221 meshing with gear 228 fixed to the end of shaft I89. From thisit will be seen that the downward movement of plunger I93 will effectcounterclockwise rotation of shaft I89 as viewed from the outer endthereof.

The plunger 282 is connected by the same form of means to a bevel gear229 which intermeshes with bevel gear 222, but in this case downwardmovement of plunger 292 will cause reverse rotation of bevel gear 222and therefore through the intervening mechanism will cause clockwiserotation of shaft I89 and thereby a reduction in the feed rate. Thebevel gear 229 is secured to a spur gear 230 which intermeshes withannular rack teeth 23I formed on plunger I91, as more particularly shownin Figure 8. Thus, the upward or downward movement is imparted toplunger I91 depending upon which of plungers I94 or-292 is depressed.

The gear 289 also meshes with a gear 232 which intermeshes witha pinion238 which is mounted for free rotation with respect to shaft I89. Thispinion has an elongated hub which projects to the outside of the machineto which is secured the rate dial 294. This dial has a beveled edge 235upon which may be scribed suitable graduations for visibly indicatingthe feed rate setting of the potentiometer.

The annular teeth 28I on plunger I91 permit rotation thereof by thereversing dogs without breaking the operating connection with gear 289and this rotation is utilized to control a revers- Ing switch forsolenoids 91 and 98 shown in Figure 5. The lower end of the plunger issplined Into a switch member 288, more particularly shown in Figures '7and 8. This switch member carries an insulated contact 281 which isconnected by a flexible lead 238 to a supply line 299. This contact isadapted to close the circuit to solenoid 98 upon clockwise rotation ofplunger 238 by engagement with contact 248 and to close the circuit tosolenoid 98 upon counterclockwise rotation by engagement with contact-The member 238 may also be manually rotated by the handle 242. Meanshave also been provided for holding the member 238'in either one of itstwo positions comprising a spring pressed detent 248 which cooperateswith a pair of indents 244 and 245 formed in the periphery of member298. From this it will be seen that the member 288 has only twopositions, both of which are running positions. Since the plunger 23Ican be moved'to a position to stop the feed motor, and since when it ismoved to this position, the feed clutch is engaged, it is possible tostop the machine automatically by use of plunger 23I which eliminatesthe necessity for providing a separate stop plunger as might ordinarilybe the case when the reversing clutch does not have a neutral position.Attention is invited to the fact that, even though the machine isstopped in this manner, still the transmission is in such condition thatrapid traverse is always available when the machine is stopped byclosing the manually operable switch 15.

It will. be recalled in connection with the description of the controldogs that the setting of the stop member I98 depended upon the positionof the previous stop member because the position in which the plungerwas put by the previous dog determines whether the ne t set- 'ting is tobe an increase or a decrease. For

this reason, it is important that after the plunger 23I has beenpositioned as by a previous dog that nothing disturb that position,because the next dog setting is dependent upon that position, and if itshould be accidentally moved to some other position the possibility ofdamage to the parts would arise. Therefore, the manual means which havebeen provided for changing the rate is so constructed that it cannot beinadvertently moved, but can only be adjusted under predeterminedconditions. This means comprises a gear 248 having an elongated hub bywhich it is journaled in the wall of the machine, the hub having clutchteeth 241 formed on one end thereof for interengagement with clutchteeth 248 formed on the boss of operating handle 249. This handle issecured to the end of a rod 249, which extends axially through thecenter of gear 248, and provided on the inner end with a cone-shapedhead 259. This head is adapted to enter a similarly shaped notch 25Iformed in the side of the interlock bar 252 This bar is pivotallyconnected at 253 to switch member 288. Since the switch member has onlythe two positions as determined by the detent 243, it will be apparentthat the bar 252 is normally in a position to prevent engagement betweenthe clutch teeth 241 and 248. Therefore to effect manual operation it isnecessary first for the operator to grasp handle 242 and move the switchmember 238 to a substantially central position and manually hold itthere while he moves the handle 249 inward to interengage clutch teeth241 and 248. Having done this, he is in a position to rotate handle 249to any desired feed rate position and then control the direction ofmovement of the table by moving handle 242. It is intended that theoperator shall continually grasp the handle 242 throughout thisoperation in order to stop the machine at any time in case.0f anyinterference between the main trip plunger and control dogs, which mightcause damage to the parts. It is primarily intended that this mechanismbe used only for set-up purposes of the machine.

In Figures 13 and 14 there are shown some typical set-ups to facilitateunderstanding or the operation of the machine and these are not to beconsidered as limiting since it is obvious to those skilled in the artthat numerous other set-ups may be made, depending upon the shape of thework and the feed rates desired at various points during the millingoperation. In Figure 13 it is assumed that a work piece, such as 254, isto be milled, the work piece having narrow portions at each end and awide portion in the middle. In this case the work piece is placed on thetable 2| to the left of the cutter as shown in Figure 1 and of courseproperly secured by suitable clamping means. The point 255 is thestopping and starting position, and therefore, once the machine isstarted the trip plunger I91 will be at the lower extreme of itstravel." In order to quickly bring the work into engagement with thecutter, the rate of travel between the point 255 and 258 will be atrapid traverse, and therefore to start the machine the operator movesthe reversing switch 242 to a central position and rotates the handle249 and thereby the shaft I89 to a rapid traverse position. In doingthis the plunger I91 is raised from its full line position to the dottedline position on ordinate 251. This will cause rotation oi shaft I89 andmovement of switch lever 16 connected therewith to a position where itwill close the circuit to the rapid traverse solenoid 13, as moreparticularly shown in Figure 3. If the operator now returns handle 242in the proper direction the table will move at a rapid traverse ratetoward the right.

It is usually desired when the cutter first engages a work piece that itdo so at a very slow rate so as to prevent undue shock to the parts.This may now be accomplished by placing a control dog on the ordinate258 which will act on plunger 282 to lower the plunger I91 and therebydecrease the rate of table movement from rapid traverse to a very lowfeed rate.

After the cutter-has started the out, the feed rate may be stepped up asby a dog placed on the ordinate 258 which will operate on plunger 184 toraise the main control plunger I81 to a position determined by the stopI98.

Having completed the narrow portion of the work piece it may be desiredto change the feed rate again as the cutter engages the wider portion ofthe work and this may be effected by placing a dog on the ordinate 268which will, through plunger l94, depress the main plunger M1 to reducethe feed rate a suitable amount. It will be obvious that this rate maybe greater than the rate established on ordinate 258, but less than therate established at ordinate 258.

When the wide portion of the work has been completed another dog may beplaced on ordinate 26! to raise the feed rate again to that equal to therate established at ordinate 259. The cutter, having finished the workat ordinate 252, a dog may be placed at this point to raise the plungerto its extreme upper or rapid traverse position and at the same timesuitably position a reversing dog to rotate plunger I91 and therebychange the direction of table movement. The table will now return at arapid traverse rate until the plunger I91 is rotated again by a secondreversing dog which will thereby change the direction of table movementand cause advance at rapid traverse rate to the ordinate 255, at whichpoint a dog may be positioned to depress the plunger to a stop position.Thus any sequence of feed rates may be obtained in a singlereciprocating cycle of the machine, and it will be noted thatthe sameplunger is utilized for effecting, not only the various feed rates, butalso the rapid traverse rate and the starting and stopping of themachine. 'Should anything go wrong during a machine cycle, the operatorhas merely to throw lever 242 to its central position and rotate lever249 to permanently stop the machine.

In Figure 14 the various dog settings are shown, if a continuousreciprocating cycle is desired, and two work pieces similar to 264 areto, be milled alternately by the cutter. In this case, the cycle foreach work piece is the same with the exception that the stop positioncorresponding to that shown at ordinate 261 in Figure 13 may beselectively utilized if it is desired to stop the machine after themilling of each work piece to insure that the operator has finishedclamping the new work piece. If it is so desired, a stop dog having apawl 283 may be utilized, this pawl having two beveled faces 26! and 265for operating plunger 282 in both directions of movement. In such a casetwo stop members I98 will be secured to the face of the dog 280 so thatwhen the trip plunger is depressed in its different rotative positions,one will cooperate with lug 203 and the other will cooperate with lug206.

The spindle transmission is shown more particularly in Figure 2 andcomprises a prime mover 266 which is mounted in a chamber 261 formed inthe base of the machine and connected, as by a belt 268, to shaft 268.'I-his shaft has splined thereto a shiftable gear 210 which is moved bya shifter fork 2' secured to.the end of shaft 212, Figure 11, which inturn is rotated by the manually operable handle 213 secured thereto.This gear is utilized for changing the direction of spindle rotation andin one position intermeshes directly with gear 214, and in its otherposition intermeshes with gear 215 which has integral therewith theidler 216 engaging gear 214.

The gear 214 is splined on shaft 211 which also has a shiftable gearcouplet 218 inthe form of back gears comprising a pinion 219 adapted tointermesh with the large gear 286 and a gear 28l adapted to intermeshwith gear 282. This conplet is shifted by a shifter fork 283 secured tothe end of shaft 284, Figure 11, having a manually operable handle 285sec'ured thereto.

The gears 282 and280 are secured on the cutter spindle 22 for effectingrotation thereof and the rate of this rotation is primarily determinedby varying the speed of motor 266 through an electrical control circuitsimilar to that shown in Figme 15 for motor 28. In other words, thiselectrical control circuit is mounted in a housing 284 carried on theside of the machine as shown in Figure 11, the potentiometer of thatcircuit being, enclosed in a housing 285 carried on the end of theoverarm 26 and connected by a suitable electric cable 286 to theelectrical devices in box 284. a

As shown in Figure 2, the potentiometer in housing 285 has a controlshaft 281 which extends through the overarm to the front end thereof,whereit is provided with a graduated dial 288 and an operating knob 288.By this means the operator can directly change the speed of rotation ofthe spindle from the front of the machine and without leaving hisoperating position. By use of the back gears, two series of rates areob. tainable sci that for light work a first series of rates is providedand for heavy Work a second series of rates is obtainable.

There has thus been provided an improved transmissionand controlmechanism for a milling machine having an improved flexible controlwhereby a series of different feed rates may be automatically obtainedduring operation of the machine and the rate of spindle rotation may bevaried from the operator's position at the front of the machine withpractically no inconvenience.

I claim:

.l. In a milling machine having a tool support and a work support, thecombination of electrical means for eifecting relative movementtherebetween which may be energized from an alternating current sourcebut speed controlled in a manner similar to direct current control,comprising an electric prime mover, a transmission train connecting theprime mover for effecting said relative movement,- circuit meanscoupling the prime mover to an alternating current source, said circuitincluding means for rectifying the current whereby the prime mover maybe of the direct current type, and a variable electrical resistancemeans remote with respect to the prime mover ,and the remainder of thecircuit for varying the speed of the prime mover'and thereby the rate ofsaid relative movement.

2. A transmission and control mechanism for effecting relative movementbetween the work support and tool support of a machine tool at differentfeeding rates, comprisingv a variable electrical resistance means, anadjustable-speed electric prime mover, means for coupling theeffective,and manually operable means located adjacent said work support foradjusting said resistance.

3. A transmission and control mechanism for effecting relative movementbetween the work support and tool support of a machine tool at differentfeeding rates, comprising a variable electrical resistance means, anadjustable-speed electric prime mover, means for coupling the primemover to an energy source which normally renders variable-resistancespeed control ineffective, said coupling means'including means forrendering variable resistance speed control means effective, manuallyoperable means located adjacent said work support for adjusting saidresistance, and dial means associated with said manually operable meansfor indicating the feed rateeifected for different adjustments of 'said'resistance.

4. In a machine tool having a cutter spindle and a work support, thecombination of a feed transmission for effecting relative movement ofthe table with respect to said spindle including an electrical primemover, a source of current, a control circuit for coupling the source tothe prime mover including variable electric resistance means for varyingthe speed of the prime mover and thereby the rate of said relativemovement, and means under control, of the table for intermittentlyvarying said resistance at predetermined points in the travel thereof tochangeti ie rate of feed during continuous movement of the table,including dogs carried by the table, and a resistance control plungeradapted to be moved predetermined amounts by said dogs in accordancewith the amount of change desired in said resistance means.

5. In a machine tool having a tool support and a work support, thecombination of means for moving one of said supports relative'to theother at a plurality of different feeding rates including a trainconnected for support movement, a direct current prime mover foractuation of the train, a source of alternating current, a rectifyingcircuit for coupling the source to said prime mover and includingadjustable resistance means capable of yielding a plurality of rates inthe prime mover, and means under control of the table and eifective onsaid circuit at predetermined points in the travel thereof forautomatically adjusting said resistance to yield new rates.

6. In a machine tool having a tool support and a work support, thecombination of variable power transmission means connected to one ofsaid supports for effecting relative movement thereof with. respect tothe other support, said transmission means includinga rate controlplunger axially movable to a plurality of positions, motion transmittingmeans coupling the plunger for varying the feeding rate yielded by saidtransmission, said plunger being movable in one direction for increasingsaid feed rate, and in an opposite direction for decreasing said feedrate; and a plurality of trip dogs positionable on the movable supportfor intermittently moving said plunger to different of said positionswhereby several feeding rates may be obtained during a singleunldirectional movement of the moving support.

7 In a machine tool having a tool support and a worksupport, thecombination of a variable feed transmission connected for effectingrelative movement between the supports, automatic control means'for'saidtransmission for varying the rate thereof including a rate controlplunger, a plurality of trip dogs. prepositionable on the table foractuation of said plunger for varying the rate of relative movementbetween the supports in one direction, additional trip clogsprepositionable on the table and effective on said plunger for varyingthe rate of movement at prescribed points during uni-directionalrelative movement I 'for stopping said feed transmission, a plurality ofcontrol dogs differently positionable on the moving support forautomatically and differently shifting said element during continuousmovement of the moving support to effect different feed rates wherebydifferent operating cycles may be obtained with the same control dogs,and an additional control dog prepositionable upon the moving supportand effective on said control element for s qpping said relativemovement.

9. In a machine tool having a work support and a tool support, thecombination of variable power transmission means for effecting relativemovement between the supports at different feed rates. including acommon control element for varying the feed rate, and for stopping andstarting the transmission; means trip operable by the moving support forautomatically changing one feed rate to any other feed rate and forstopping the feed movement; and manually operable means for positioningsaid control element to start the feed transmission.

10. A machine tool having a work support, a tool support, a variablefeed transmission for effecting relative movement between said supports,control means for varying the rate of said transmission, including acontrol element prepositionable to adjust said transmission to yield agiven feed rate; a rapid traverse transmission; means to connectautomatically the rapid traverse transmission for subsequent movement ofthe support at a rapid traverse rate, and means to automaticallydisconnect the rapid traverse transmission, and reconnect the feedtransmission for support movement but at a different rate than saidgiven feed rate. 1

11. In a machine tool having a work support and a tool support, thecombination of transmission means for effecting relative movementtherebetween including a reverser mechanism having a control membermovable to two different power transmitting positions for yieldingopposite directions of support movement, means normally operable tomaintain said control member in one or the other of its powertransmitting positions, a variable feed transmission for actuating saidsupport through thereverser, manually operable rate control means forsaid transmission, and means restraining operation of said manuallyoperable means while the reverser is in either one of its powertransmitting positions.

12. In a machine tool having a work support and a tool support, thecombination of transmission means for efiecting relative movementtherebetween including a reverser mechanism having a control membermovable to. two different power transmitting positions for yieldingopposite directions of support movement, means normally operable tomaintain said control member in one or the other of its powertransmitting I positions, a variable feed. transmisison for actuatingsaid support through the reverser, manually a tool support, a variablefeed transmission for effecting relative movement between the supportsand including a rate control member coupled for increasing the rate ofsaid transmission upon movement in one direction, and for decreasing therate of the transmission upon movement in the opposite direction, afirst trip dog carried by the movable support, motion transmitting meansoperable by the dog for moving said control element in one direction; asecond trip dog, and

motion transmitting means operable thereby for moving said controlelement in an opposite direction.

14. A milling machine having a column, a

tool spindle journaled in the column, a work table supported by thecolumn for movement transversely to the axis of said spindle, a feedtransmission and a rapid traverse transmission for effecting saidmovement, a feed-rapid traverse selector clutch, a control membercoupled for varying the rate of the feed transmission and means operableby said control member for shifting said selector clutch.

15. In a machine tool having a tool spindle, and a work support movablerelative thereto, the combination with a feed transmission and a rapidtraverse transmission for effecting said movement, of a common controlmember, means operable by said member to start and stop said feedtransmission and to vary the feed rate thereof, and additional meanscontrolled by said member to selectively connect the rapid traversetransmission for actuation of the moving part.

16. A machine tool having a work support, a tool spindle, means foreffecting relative move- 5 ment between the parts including a feedtransmission, a rapid traverse transmission, control means thereforincluding a rotatable shaft having a first position for stopping saidfeed transmission, a second position for starting the feed transmission,a plurality of successive positions for increasing the rate of said feedtransmission step-by-step, and a final position for disconnecting thefeedtransmission and connecting the rapid traversetransmission foractuation of the moving part.

17. In a machine tool having a work'support and a tool support, thecombination with a variable feed rate transmission for effecting saidmovement, of a rate variator movable in one direction to increase thefeed rate and in a second direction to decrease the feed rate, and apair of trip operable plungers adjacent the moving support andoperatively coupled with said rate variator for respectively increasingand de- 7 creasing said rate automatically.

18. In a machine tool having a cutter spindle, and a work table movablerelative thereto, the combination with a variable feed transmission foreffecting table movement, of a rate variator movable in oppositedirections to increase and decrease respectively the rate of saidtransmission, a pair of trip operable plungers adjacent the table andoperatively connected for effecting the respective movements of thevariator, and prepositionable means for limiting the movement impartedto the variator by the respective plungers.

19. In a machine tool having a cutter spindle and a work support, thecombination with a variable feed transmission for effecting relativemovement between the work support and tool spindle at different feedingrates, 'of a rate variator coupled for control of said transmissionincluding an operating shaft movable in one direction to increase therate, and in the other direction to decrease the rate, a pair of tripoperable plungers adjacent the table .for dog actuation thereby,uni-directional clutch means connecting the plungers to said shaft,means operable by one of said clutch means to efiect rotation of theshaft in one direction, means opera.- ble by the otherclutch means toeffect rotation of the shaft in the opposite direction, and means toreturn i the respective plungers after each actuation of its respectiveclutch means.

20. In a machine tool having a work support and a tool support thecombination with a variable feed transmission for effecting relativemovement between said supports, of a feed rate changer operativelyconnected with said transmission for varying the output rate thereof,said variator including a control member movable in one direction toincrease the output rate, and in an opposite direction to decrease theoutput rate, a first uni-directionally operable mechanism for moving themember in one direction, a second uni-directionally operable mechanisrrffor moving the member in an opposite direction, said mechanismsterminating in trip operable devices adjacent the movable support. andindividual trip dogs carried by the moving support for operating saidtrip operable devices 21. In a machine tool having a work support and atool support the combination with a variable feed transmission forefiecting relative movement between said supports, of a feed ratechanger operatively connected with said transmission for varying theoutput rate thereof, said variator including a control member movable inone direction to increase the. output rate, and in an opposite directionto decrease the output rate, a first uni-directionally operablemechanism for moving the member in one direction, a seconduni-directionally operable mechanism for moving the member in anopposite direction, said mechanisms terminating in trip operable devicesadjacent the movable support, individual trip dogs carried by the movingsupport for operating said trip operable devices, and prepositionablemeans associated with the respective trip dogs for lim-- iting themovement imparted to each mechanism.

22. A machine tool having a support, a tool spindle journaled in thesupport, a work table carried by the support for movement transverselyof the spindle, a variable feed transmission for effecting saidmovement, control means operatively coupled for varying the rate of saidtransmission including a control plunger mounted on the support inadjacent relation to the table, said plunger being rotatable to a firstposition for controlling the rate of table movement in one direction,and to a second position for controlling the rate of table movement inan opposite direction, said plunger being axially movable in eitherposition to increase or decrease the feed rate, a first lug on theplunger for limiting its axial movement in either direction, when in onerotative position, and a second lug thereon for limiting its movementwhen in its other rotative position.

23. In a machine tool having a cutter, a work support and a variablefeed transmission for effecting relative movement between the worksupport and cutter, the combination of control means for varying therate of said transmission including a rate control plunger axiallymovable in opposite directions to increase or decrease the rate, and atripping device prepositionable on the table having a first part foreffecting movement of the plunger, and a second part for limiting themovement of the plunger to any desired extent whereby a subsequent ratemay be determined automatically.

24. In a machine tool having a cutter spindle and a work support thecombination with transmission means for effecting relative movementbetween the work support and cutter spindle selectively at feeding orrapid traverse rates, of control means for said transmission including amovable control member, means operable thereby when in one extremeposition to stop said relative movement, means operable thereby when inits other extreme position to effect rapid traverse movement of the worktable, and means operable thereby when in intermediate positions to varythe feeding rate of said work table.

25. In a machine tool having a cutter spindle and a work support thecombination with transmission means for efiecting relative movementbetween the work support and cutter spindle selectively at feeding orrapid traverse rates, of control means for said transmission including amovable control member, means operable thereby when in one extremeposition to stop said relative movement, means operable thereby when inits other extreme position to effect rapid traverse movement of the worktable, means operable thereby when in intermediate positions to vary thefeeding rate of said work table, a first trip plunger, means operativelyconnected thereto to efliect movement ofthe control plunger toward oneextreme position, a second trip plunger, means connected thereto foreffecting movement of the control plunger towards the other extremeposition, and trip dogs prepositionable upon the table for operatingeach of said plungers.

26. A milling machine having a column, a cutter spindle journaled in thecolumn, means carried'by the column for supporting a work piece forrelative movement with respect to said spindle, and means for variablyrotating said spindle including a direct current electric motor, analternating current source, a rectifying circuit coupling the motor tosaid source, electrical resistance means in said circuit for varying thespeed of the motor and thereby of the spindle and manual operable meanslocated at a control sta-..

tion of the machine for adjusting said resistance.

27. A machine tool having a work support, a tool support, a feed on foreffecting relative movement between the supports including a memberadjustable for obtaining a plurality of feed rates and cooperatingmembers, one of which is carried by the moving support and the otheroperatively connected to said adjustable member whereby during travel ofthe movable support one of said cooperating members will shift the otherto change the feed rate, and additional transmission means for effectingrelative movement between the supports at a rapid traverse rate, andmeans to selectively connect said additional transmission for efiectingsaid.

relative movement at a fast rate.

28. In a milling machine having a tool spindle support, and a worksupport, the combination of transmission means-for effecting relativemovement between the supports at a feeding rate, said transmission beingvariable to yield a first feeding rate, a second feeding rate, and aplurality of other feeding rates, trip dogs adapted to-be selectivelypositioned on the moving support in different spaced relation to obtaindifferent operatingcycles, and a rate change mechanism including a partmovable to effect a change from any of said rates to any other thereof,said mechanism also including portions adjacent the moving support forintermittent engagement by said trip dogs for automatically shiftingsaid part from any one of its rate positions to any other thereof inaccordance with the cyclic positioning of said trip dogs.

29. In a milling machine having a tool spindle support and a worksupport, the combination of a variable feed transmission means foreffecting relative movement between the supports at a feeding rate, saidtransmission being variable to yield a first feeding rate, a secondfeeding rate and a plurality of other feeding rates, trip dogs adaptedto be selectively positioned on the moving support in different spacedrelation to obtain difierent opera ing cycles, a rate change mechanismincluding a part movable to effect a change from any of said rates toany other thereof, said mechanism also including portions adjacent saidsupport for intermittent engagement by said trip dogs for automaticallyshifting said part from any of its rate positions to any other thereofin accordance with the cycle positioning of said trip dogs, and meansfor maintaining said part in any of its rate positions after the tripdogs have passed out of contact with said portions.

30. A milling machine having a work support, a cutter support, and apower feed transmission for effecting relative movement between thesupports comprising a final train coupled to the movable support, adirect current prime mover for actuating the train, means to supplyenergy to the prime mover from an alternating current source including arectifying circuit having variable electrical resistance means thereinfor varying the speed of a prime mover and thereby the rate of themoving support, and means to automatically change said speed from themovement of said support including a control member movable to vary saidelectrical resistance means, a plurality of trip dogs adapted to bevariably spaced on said support to determine the points in supporttravel where changes in rate are to be eii'ected, and means momentarilyengageable by said trip dogs during their travel with the support toshift said control member .variable amounts in accordance with therequired amount of variation in rate.

- 31. In a machine tool having a tool support and a work support, thecombination with a variable speed power transmission for eifectingvariable rates of feeding movement between said sup- P rts, of a movablerate variator for said transmission, means to normally frictionallystabilize the position of said variator in any given rate positionthereof. a trip control mechanism in-- cluding a pair of plungerslocated in different planesparallel to the direction of table movementoperatively connected to said rate variator for moving the samerespectively in opposite directions, and diiferent trip dogs selectivelypositionable upon the table for engaging said plungers to causeselective adjustment oi said control member in either direction, wherebythe rate of the moving support may be automatically mcreased ordecreased.

32. In a machine tool having a movable support, a. variable feed powertransmission for moving said support, and a rate control memberoperatively coupled with said transmission and movable in oppositedirections to increase or decrease the output rate of said transmission,the combination of meansfor automatically shifting said control memberat various instantaneous positions of said support during continuoustravel thereof, including a plurality of trip dogs preposltionable onthe table at prescribed points, a pair of trip plungers operativelyconnected to said control member and adapted to be selecg tively engagedby said trip dogs, one of said plungers operating to increase the rateof movementof said support and the other to decrease the rate ofmovement of said support, and adjustable means associated with each dogfor predetermining the amount of movement to be imparted thereby to therate control member.

33. A machine tool having a work support, a tool support, a variableteed transm'"slon for effecting relative movement between said supportsincluding an adjustable rate control elernent, said element having aplurality of 'diilerent positions for deriving from said transmission aplurality of difierent feed rates, said element having an additionalposition for stopping said feed transmissioina plurality of control dogsprepositionable in variable spaced relation on the moving support forautomatically shifting said element difierent amounts in oppositedirections

